The related-art in-wheel motor drive device is described in, for example, JP 2012-148725 A (Patent Document 1). The in-wheel motor drive device described in JP 2012-148725 A includes a motor part configured to generate driving force, a wheel bearing part to be connected to a wheel, and a speed reduction part arranged between the motor part and the wheel bearing part and configured to reduce a speed of rotation of the motor part to transmit the rotation to the wheel bearing part.
In the above-mentioned in-wheel motor drive device, a low-torque high-rotation motor is utilized in the motor part from the viewpoint of device compactness. Meanwhile, the wheel bearing part requires a large torque for driving the wheel. Therefore, a cycloid reducer capable of obtaining a high speed reduction ratio with a compact size is utilized.
The motor part is a radial gap motor including a stator fixed to a casing, a rotor arranged inside the stator at an opposed position with a radial gap, and a rotation shaft of the motor, which is connected and fixed to the inside of the rotor to rotate integrally with the rotor. Both axial ends of the rotation shaft of the motor having the hollow structure are rotatably supported on the casing by a pair of rolling bearings.
The speed reduction part in which the cycloid reducer is utilized mainly includes an input shaft of the speed reducer having a pair of eccentric parts, a pair of curved plates arranged at the eccentric parts, respectively, a plurality of outer periphery engagement members configured to engage with outer peripheral surfaces of the curved plates to cause rotational motion of the curved plates, and a plurality of inner pins configured to transmit the rotational motion of the curved plates to an output shaft of the speed reducer. The above-mentioned rotation shaft of the motor is spline-connected to the input shaft of the speed reducer.